1. Field of the Invention
The present invention relates to an ink-jet printing apparatus that jets at least two different types of inks having different densities with respect to a plurality of ink colors, as well as to an ink reservoir unit attached to such an ink-jet printing apparatus.
2. Description of the Related Art
Color printers with a print head that jets inks of plural different colors have been widely used as the output apparatus of the computer that prints the image processed by the computer in a multi-color, multi-tone form. FIG. 21 illustrates an ink-jet head 100 included in such a printing apparatus. The ink-jet head 100 includes a black ink nozzle array K.sub.D for jetting black ink, a deep cyan ink nozzle array C.sub.D for jetting deep cyan ink, a light cyan ink nozzle array C.sub.L for jetting light cyan ink, a deep magenta ink nozzle array M.sub.D for jetting deep magenta ink, a light magenta ink nozzle array M.sub.L for jetting light magenta ink, and a yellow ink nozzle array Y.sub.D for jetting yellow ink. The number of nozzles included in each nozzle array is, for example, 32.
The first capital alphabet included in the symbol showing each nozzle array represents the ink color. The subscript `D` denotes the ink of a comparatively high density, and the subscript `L` denotes the ink of a comparatively low density. The subscript `D` in the yellow ink nozzle array Y.sub.D implies that gray color is made by mixing substantially equal amounts of the yellow ink jetted from this nozzle array, the deep cyan ink, and the deep magenta ink. The subscript `D` in the black ink nozzle array K.sub.D implies that the black ink jetted from this nozzle array is not gray but black having the density of 100%.
A plurality of nozzles included in each nozzle array are aligned in a sub-scanning direction SS. The six nozzle arrays are arranged in such a manner that six nozzles for jetting six different inks are aligned in one straight line extending in a main scanning direction MS. The alignment of the six nozzles for jetting six different inks in the main scanning direction MS prevents deterioration of the picture quality due to misalignment of the dots of different colors in the sub-scanning direction.
Color printing requires a significantly longer time period than black and white printing. It is thus highly demanded to increase the number of nozzles for each ink, in order to improve the speed of color printing.
In the conventional arrangement, the nozzles for all the inks are formed in one ink-jet head 100. The arrangement of the ink-jet head in which an extremely large number of nozzles are formed, however, lowers the manufacturing yield. The desired printing apparatus has an ink-jet head that effectively prevents deterioration of the picture quality due to misalignment of dot formation positions in the main scanning direction even in the case of an increased number of nozzles formed in the ink-jet head and that is readily manufactured.
It is here assumed that natural images, such as photographs of landscape and portrait, are printed by a printing apparatus that uses inks of comparatively high densities and inks of comparatively low densities for specific colors (cyan and magenta in the example of FIG. 21). In this case, the positional accuracy of the impact area (that is, the accuracy of the position where ink jetted from the ink-jet head impacts on a printing medium) especially with respect to the inks of comparatively low densities significantly affects the picture quality of a printed image. The low positional accuracy of the impact area with respect to the inks of comparatively low densities undesirably causes banding and harshness in low-density areas, which are often included in the natural images, and thereby deteriorates the picture quality. The arrangement of the ink-jet head in which an extremely large number of nozzles are formed with the high positional accuracy of the impact area of the inks jetted therefrom further lowers the manufacturing yield.